Various sensor systems have been developed for detecting sheet properties “on-line,” i.e., on a sheet-making machine while it is operating. Sensors for continuous flat sheet production processes typically employ single or dual-sided packages with on-line sensors that traverse or scan traveling webs of sheet material during manufacture. With dual scanners, the heads or assemblies are fixed to beams that span both sides of the sheet with linear guidance tracks to allow the sensors to move in unison in the cross direction, i.e., in the direction perpendicular to the direction of sheet travel. Depending upon the sheet-making operation, cross-directional distances can range up to about twelve meters or more. In the paper making art, for instance, the on-line sensors detect variables such as basis weight, moisture content, and caliper of sheets during manufacture.
The electronics in the enclosed scanner heads generate heat that must be dissipated. In addition, paper and continuous web scanners are often operated at varying and high temperature conditions. Thermal loading originate from a myriad of sources in the proximity of the scanner that cause ambient air temperature gradients between the beams that are positioned above and below the sheet of paper. Major contributors include hot or cold air sources, such as exterior doors, openings to cold basements, and hot drier exits, and directional heating from infrared radiation sources typically used to dry coatings on sheets. The temperature fluctuations adversely affect the sensors. Current scanners have external coolant sources that continuously supply circulating coolant to internal cooling channels within the scanner heads. These external coolant sources however are permanently connected to the scanner heads as the latter travels back and forth during operations. The associated connections add to the complexity and costs of the scanning systems and adversely affect the measurement accuracy of the scanners.